Passenger transportation devices such as escalators and moving walks are generally-known and efficient devices for the transportation of people. Escalators are typically used to transport people in the vertical direction, for example from one story of a building to another story, while moving walks are mostly used for the transportation of people in the horizontal direction, or with a slight incline of up to 12°, from one point to another point. The length and the width of the passenger transportation device are chosen depending on the expected passenger traffic in the respective application.
Escalator steps and pallets are designed as monolithic or multi-part components and normally manufactured by a casting, extrusion, or forging method. The upper side of the tread-elements of steps and pallets has a tread pattern in the form of a sequence of parallel ribs or ridges that run from the front-side to the back-side of the tread-element. Hence, the ribs extend in the foreseen direction of movement of the step or pallet. In the case of escalator steps, also their riser elements have ribs, which normally adjoin the ribs of the tread-elements. Further, the ribs are dimensioned to engage with the comb-structures that are arranged in the boarding areas of the escalator or moving walk.
By means of at least one traction means, a plurality of steps is combined into a step-band of an escalator. In the same manner, a plurality of pallets is combined into a pallet-band. A moving walk or an escalator normally has a frame, or truss, with two reversing zones, between which the pallet-band or the step-band respectively is guided in circulating manner.
If the pallets or steps are manufactured in one piece from cast or die-cast aluminum, or from another suitable metal or a metal alloy, an extensive set of molds, jigs, and tools must be available, since each width of the pallet-band or of the step-band requires its own mold. The molds for pallets and steps are, however, very expensive. Further, the size of these molded parts, in particular the tread-element with its ribs, can result in casting problems, namely that of cavity formation, to avoid which an elaborate tempering of the molds is necessary.
To solve this problem, EP 1 755 999 B1 proposes a modular construction of pallets, so that the various widths of the pallets can be manufactured with fewer, and smaller, molds. The pallets consist essentially of a die-cast supporting body of aluminum and of a plurality of tread-elements. The tread-elements are fastened to the supporting body by means of fastening protrusions, which protrude into the supporting body, and a locking element. A first disadvantage of this solution is that, despite the spring elements that are arranged between the tread-elements and the supporting body, through vibrations and shocks which inevitably occur during operation, unpleasant noises can occur as a consequence of relative movements between the tread-elements and the supporting body when the vibrations are in the range of the resonant frequency of this vibration system of spring element and tread-elements. Further, after a certain period of use, the spring element can display symptoms of subsidence, since it is stressed by the users each time they board. The damping element, which is proposed as alternative to the spring element and arranged between the tread-plates and the supporting body, also has disadvantages. As a consequence of the repeated loading of the tread-plates by users, and the vibrations that are present, these damping elements of plastic can be rubbed between the tread-plate and the supporting body. In addition, lubricants that are present in escalators and moving walks, which are particularly used in the area of the pallet-band or step-band, can also decompose these plastic damping elements.
Further, in the presence of a spring element or damping element, the mounting of the tread-elements on the supporting body is quite elaborate, since, in the case of a multi-part tread-element, all tread-elements must be pressed against the supporting body simultaneously, in order that a lateral insertion of the bolt, or a turning of the excenter, is at all possible.